A flange connection of this type is known, for example, from German Offenlegungsschrift No. 22 21 312. In the case of this known flange profile there is fitted between the second web of the bead and the first longitudinal arm a seal which is intended to prevent air passing through the gap between the first longitudinal arm and the inside of the duct wall and then over the end face of the duct wall and to the outside. Such a seal which is located inside the hollow profile cannot however be sufficiently reliable in use. In fact, the only feasible solution is an injected sealing composition. As the flange profiles are sometimes of quite considerable length, however, it is impossible to ensure a sufficiently quantity of sealing composition being present everywhere along this cavity. Therefore, it is not possible adequately to ensure the intended sealing effect. In addition, even with permanently elastic seals, their elasticity can only be retained for a limited time, particularly in elevated working temperatures which, in the case of air conditioning ducts, may be as much as 60.degree. C., so that they rapidly lose their sealing effect.
German Auslegeschrift No. 23 13 425 likewise discloses a flange connection of the type mentioned at the outset. In the case of the flange profile shown therein, the second web of the bead forms together with the first longitudinal arm a wedge-shaped slot into which it is intended that the end face of the duct wall should be clampingly inserted. Accordingly, the sealing action is intended to be established along the end edge of the duct wall. In practice, however, this causes considerable difficulties because above all these end edges of the duct walls diverge greatly from what is the ideal straight line. Thus they exhibit varying degrees of burr formation and in addition have become misshapen due to relatively rough handling in transport and at the assembly site. Furthermore, the construction of profile illustrated is extremely unfavourable from the manufacturing point of view. This narrow wedge-shaped groove calls for correspondingly narrow rolling and the rollers are subjected to an enormous loading. The sheet metal undergoes extreme deformation particularly in the region of the bead, which on the one hand denotes considerable wear and tear on the rolling tools and on the other considerable likelihood of fracture in the overstressed material. This is disadvantageous in that air conditioning ducts are caused to undergo considerable oscillation due to currents of air in the low frequency and high frequency vibration range. In order to avoid damage resulting therefrom, it is necessary to follow the rolling operation on the flange profile with either some annealing process or a heavily stressable and thus more expensive material must be used in its manufacture. The wedge-shaped surface cannot be produced in any technologically feasible arrangement.